PROJECT SUMMARY A long-held view is that gene regulatory complexity in stem cells and development is achieved through the judicious organization of millions of enhancer elements. A recently identified new class of DNA binding fac- tors called THAPs (Thanatos-associated domain-containing apoptosis-associated proteins) may provide new insights into gene regulation in stem cells. One key member of this family, Ronin (Thap11), was discovered by us in embryonic stem cells. Ronin is expressed during the earliest stages of embryonic development and is essential for the maintenance of stem cell pluripotency, both in vitro and in vivo. Since Ronin lacks appreciable transac- tivation activity but functions as a DNA-binding nuclear protein with strong protein dimerization activity, we considered that it may not act in the classical manner of a transcriptional regulator (e.g., having an acidic activa- tion domain) but instead might augment gene expression by facilitating communication among Ronin binding sites through DNA looping. This working hypothesis gained traction when we found that most (83%) of the looping events mediated by Ronin involve promoter-to-promoter links rather than the enhancer-to-promoter interactions seen with typical transcription factors. In this research study we will (i) establish the effects of Ro- nin-mediated promoter tethering on transcription and gene regulation in stem cells; (ii) determine the influence of promoter tethering on developmental transitions especially from the nave to primed pluripotent state; and (iii) ask if other THAPs participate in development specific gene clustering as well.